1. Field of the Invention
The present invention relates generally to an asynchronous CDMA mobile communication system, and in particular, to an apparatus and method for transmitting TFCI (Transport Format Combination Indicator) bits used during data transmission over a downlink shared channel in an asynchronous CDMA mobile communication system.
2. Description of the Related Art
In general, a downlink shared channel (DSCH) is shared by a plurality of users on a time-division basis. The DSCH is established in association with a dedicated channel (DCH) for every user. The DCH is transmitted over a dedicated physical channel (DPCH), and the DPCH is constructed by combining a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH) on a time-division basis.
The DSCH is transmitted over a physical downlink shared channel (PDSCH), and channel control information for the PDSCH is transmitted over DPCCH in the DPCH. The control information transmitted over the DPCCH includes information on (i) TPC (Transmitted Power Control command) for controlling uplink transmission power from a UE (User Equipment), (ii) Pilot field used for channel variation estimation, transmission power measurement, and slot synchronization acquisition from a Node B to a UE, and (iii) TFCI (Transport Format Combination Indicator). Of this information, the TPC and the Pilot are used as physical control information for the PDSCH and the DPCH, and the TFCI is used to indicate information characteristics (e.g., information transfer rate, and combination of different information, i.e., combination of voice information and packet information) of the data transmitted over the DSCH and the DPDCH.
As stated above, the TFCI, the control information indicating information characteristics of the data transmitted over the physical channels DSCH and DPDCH, has a 10-bit length and is encoded into 32 bits. That is, information on an amount of data is expressed with 10 bits, and the 10-bit information is encoded into 32 bits to be transmitted over the physical channel.
The TFCI is transmitted over the physical channel in the following method specified in the 3GPP (3rd Generation Partnership Project) Technical Specification 25.212 for UMTS (Universal Mobile Telecommunication System).                ak=kth information bit of transport combination information (0≦k≦9)        bl=ith coded bit of transport combination information (0≦l≦31)        dm=mth transmitted coded bit of transport combination information        
The ak is 10-bit information indicating rate, type and combination of the data transmitted over the DPDCH, the bl is comprised of 32 coded bits obtained by encoding the ak, and the dm is a transmitted coded bit where the bl is transmitted over the DPCCH. Here, the value m is variable according to conditions.
Conditions for determining the number of dm bits are determined based on a transmission mode of the DPCCH and a data rate of the DPCH. The transmission mode of the DPCCH includes a normal transmission mode and a compressed transmission mode. The compressed transmission mode is used when a UE having one RF transceiver intends to measure at another frequency band. An operation in the compressed transmission mode temporarily suspends transmission at the current frequency band enabling the UE to measure at another frequency band. Data to be transmitted in the transmission suspended period is compressed immediately before and after the transmission suspended period.
The “data rate of the DPCH”, one of the conditions for determining the number of dm bits, refers to a physical data rate of the DPCH and is determined according to a spreading factor (SF) of data. In the 3GPP of the current mobile communication standard, the SF ranges from 512 to 4 and the data rate ranges from 15 Kbps to 1920 Kbps. As the SF becomes higher, the data rate becomes lower. The reason that the number of dm bits is determined according to the data rate of the DPCH is because the size (or length) of the TFCI field transmitting TFCI bits of the DPCCH is variable according to the data rate of the DPCH.
The number of dm bits transmitted for each of the conditions for determining dm is calculated as follows.
A1. Normal Transmission Mode, Data Rate of DPCH Being Lower than 60 Kbps
In the case of a condition A1 for determining the number of dm bits, the number of dm bits becomes 30. In the 3GPP standard, a basic transmission unit of the physical channel is a radio frame. The radio frame has a length of 10 ms and is comprised of 15 time slots. Each time slot has fields for transmitting TFCI. In the case of A1, each time slot has 2 TFCI transmission fields, so the number of TFCI transmission code bits dm that can be transmitted for one radio frame becomes 30. Therefore, although the number of the coded bits bl based on the information bit ak becomes 32, the last two transport combination information bits b30 and d31 are not transmitted due to a limitation in the number of the TFCI fields actually transmitted.
A2. Normal Transmission Mode, Data Rate of DPCH Being Higher than 60 Kbps
In the case of a condition A2 for determining the number of dm bits, a length of the TFCI field in the time slot becomes 8 bits, and the total number of dm that can be transmitted over the DPCCH for one radio frame becomes 120. When the total number of dm is 120, bl is repeatedly transmitted, as follows.d0(b0), . . . , d31(b31), d32(b0), . . . , d63(b31), . . . , d96(b0), . . . , d119(b23)
In the case of A2, 0th to 23rd bl bits are repeated 4 times, and 24th to 31st bl bits are repeated 3 times for transmission.
A3. Compressed Transmission Mode, Data Rate of DPCH Being Lower than 60 Kbps or Equal to 120 Kbps
In the case of a condition A3 for determining the number of dm bits, a length of the TFCI field in the time slot becomes 4 bits, and the number of TFCIs that can be transmitted for one radio frame is variable according to the number of time slots used in the compressed transmission mode. In the compressed transmission mode, the number of transmission-suspended time slots ranges from a minimum of 1 to a maximum of 7, and the number of dm bits is between 32 and 56. The number of the transmitted coded bits dm is limited to a maximum of 32, thereby to transmit all of 0th to 31st bl bits at the changed dm, and not transmit the bl bits at the other dm.
A4. Compressed Transmission Mode, Data Rate of DPCH Being Higher than 120 Kbps or Equal to 60 Kbps
In the case of a condition A4 for determining the number of dm bits, a length of the TFCI field in the time slot becomes 16 bits, and the number of TFCIs that can be transmitted for one radio frame is variable according to the number of time slots used in the compressed transmission mode. In the compressed transmission mode, the number of transmission-suspended time slots is a minimum of 1 to a maximum of 7, and the number of dm bits ranges from 128 to 244. The number of the transmitted coded bits dm is limited to a maximum of 128, thereby to repeatedly transmit 0th to 31st bl bits 4 times at the changed dm, and not transmit the be bits at the other dm.
In the compressed transmission mode of A3 and A4, the dm bits are arranged in a period as far away from the transmission suspended period as possible to maximize reliability of transmitting the dm bits.
The A1, A2, A3 and A4 conditions are used when the TFCI indicates the transport combination and type of the DPCH. A method of dividing the TFCI into TFCI for DSCH and TFCI for DPCH during transmission can be divided into two separate methods.
A first method is a method for a hard split mode (HSM), and a second method is a method for a logical split mode (LSM).
The TFCI for DCH will be referred to as TFCI(field 1) or a first TFCI, and the TFCI for DSCH will be referred to as TFCI(field 2) or a second TFCI.
In the LSM method, the TFCI(field 1) and the TFCI(field 2), as one TFCI, are encoded with a (32,10) sub-code of the second order Reed-Muller code. The TFCI(field 1) and the TFCI(field 2) express 10-bit TFCI information in various ratios, and the 10 information bits are encoded with one block code, i.e., (32,10) sub-code of the second order Reed-Muller code according to the A1, A2, A3 and A4 conditions, before being transmitted. The ratios of the TFCI(field 1) to the TFCI(field 2) include 1:9, 2:8 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1.
In the HSM method, the TFCI(field 1) and the TFCI(field 2) are fixedly expressed with 5 bits, respectively, and each information is output using a (16,5) bi-orthogonal code, and then the 16 bits for the TFCI(field 1) and the TFCI(field 2) are alternately transmitted in accordance with the A1, A2, A3 and A4 conditions.
FIG. 1 illustrates a structure of a transmitter based on the conventional HSM method. Referring to FIG. 1, a (16,5) bi-orthogonal encoder 100 encodes a 5-bit TFCI(field 1) for the DCH into 16 coded symbols, and provides the 16 coded symbols to a multiplexer 110. At the same time, a (16,5) bi-orthogonal encoder 105 encodes a 5-bit TFCI(field 2) for the DSCH into 16 coded symbols, and provides the 16 coded symbols to the multiplexer 110. The multiplexer 110 then time-multiplexes the 16 coded symbols from the encoder 100 and the 16 coded symbols from the encoder 105, and outputs 32 symbols after arrangement. A multiplexer 120 time-multiplexes the 32 symbols output from the multiplexer 110 and other signals, and provides its output to a spreader 130. The spreader 130 spreads the output signal of the multiplexer 120 with a spreading code provided from a spreading code generator 135. A scrambler 140 scrambles the spread signal with a scrambling code provided from a scrambling code generator 145.
FIG. 2 illustrates a general procedure for exchanging signaling messages and data between a Node B and RNCs (Radio Network Controllers) for the HSM method defined in the 3GPP (3rd Generation Partnership Project). A 3GPP RAN (Radio Access Network) is comprised of a RNC (Radio Network Controller), a Node B controlled by the RNC, and a UE (User Equipment). The RNC controls the Node B, the Node B serves as a base station, and the UE serves as a terminal. The RNC can be divided into an SRNC (Serving Radio Network Controller) and a CRNC (Control Radio Network Controller) according to the relationships with the UE. The SRNC, an RNC where the UE is registered, processes data to be transmitted to and received from the UE, and controls the UE. The CRNC, an RNC where the UE is currently connected, connects the UE to the SRNC.
Referring to FIG. 2, if transmission data of the DSCH is generated, a radio link controller (RLC) 11 of an SRNC (Serving RNC) 10 transmits the DSCH data to a MAC-D (Medium Access Control-Dedicated channel) 13 of the SRNC 10 in step 101. A primitive transmitted at this moment is MAC-D-Data-REQ. In step 102, the MAC-D 13 of the SRNC 10 transmits the DSCH data received from the RLC 11 to a MAC-C/SH (MAC-Common/Shared channel) 21 of a CRNC (Control RNC) 20. A primitive transmitted at this moment is MAC-C/SH-Data-REQ. In step 103, the MAC-C/SH 21 of the CRNC 20 determines (schedules) a transmission time for the DSCH data received in the step 102 from the MAC-D 13 of the SRNC 10, and then, transmits the DSCH data along with its associated TFI (Transport Format Indicator) to an L1 (Layer 1) 30 of a Node B (hereinafter, the term “Node B” refers to a base station). A primitive transmitted at this moment is MPHY-Data-REQ. In step 104, the MAC-D 13 of the SRNC 10 transmits transmission data of the DCH and its associated TFI to the L1 30 of the Node B. A primitive transmitted at this moment is MPHY-Data-REQ. The data transmitted in the step 103 is independent of the data transmitted in the step 104, and the L1 30 of the Node B generates a TFCI that is divided into a TFCI for the DCH and a TFCI for the DSCH. In the steps 103 and 104, the data and the TFIs are transmitted using a data frame protocol. After receiving the data and the TFIs in steps 103 and 104, the L1 30 of the Node B transmits the DSCH data over a physical DSCH (PDSCH) to an L1 41 of a UE (User Equipment; hereinafter, the term “UE” refers to a mobile station) 40 in step 105. Thereafter, in step 106, the L1 30 of the Node B transmits the TFCI to the L1 41 of the UE 40 using the DPCH. The L1 30 of the Node B transmits the TFCIs created with the TFIs received in the steps 103 and 104, using the fields for the DCH and the DSCH.
FIG. 3 illustrates a general procedure for exchanging signaling messages and data between a Node B and RNCs for the LSM method. Referring to FIG. 3, if DSCH data to be transmitted is generated, an RLC 301 of an RNC 300 transmits the DSCH data to a MAC-D 303 of the RNC 300 in step 201. A primitive transmitted at this moment is MAC-D-Data-REQ. Upon receipt of the DSCH data from the RLC 301, the MAC-D 303 transmits the DSCH data to a MAC-C/SH (MAC-Common/Shared channel) 305 in step 202. A primitive transmitted at this moment is MAC-C/SH-Data-REQ. Upon receipt of the DSCH data, the MAC-C/SH 305 determines (schedules) a transmission time of the DSCH data and then transmits a TFCI associated with the DSCH data to MAC-D 303 in step 203. After transmitting the TFCI to the MAC-D 303 in the step 203, the MAC-C/SH 305 transmits the DSCH data to an L1 307 of the Node B in step 204. The DSCH data is transmitted at the time determined (scheduled) in the step 203. Upon receipt of the TFCI for the DSCH data transmitted from the MAC-C/SH 305 in the step 203, the MAC-D 303 determines a TFCI for the DSCH and transmits the TFCI to the L1 307 of the Node B in step 205. A primitive transmitted at this moment is MPHY-Data-REQ. After transmitting the TFCI for the DSCH, the MAC-D 303 determines a TFCI for the DCH and transmits the DCH data along with the TFCI for the DCH to the L1 307 of the Node B in step 206. A primitive transmitted at this moment is MPHY-Data-REQ. The DSCH data transmitted in the step 204 and the TFCI transmitted in the step 205 are related to the time determined in the step 203. That is, the TFCI in the step 205 is transmitted to a UE 310 over the DPCCH at a frame immediately before the DSCH data in the step 204 is transmitted over the PDSCH. In the steps 204, 205, and 206, the data and the TFCIs are transmitted using a frame protocol. Particularly, in the step 206, the TFCI is transmitted through a control frame. In step 207, the L1 307 of the Node B transmits the DSCH data over the PDSCH to an L1 311 of the UE 310. In step 208, the L1 307 of the Node B creates a TFCI using the respective TFCIs or TFIs received in the steps 205 and 206, and transmits the created TFCI to the L1 311 using the DPCCH.
Summarizing the LSM method, the MAC-C/SH 305 transmits DSCH scheduling information and TFCI information of the DSCH to the MAC-D 303 in the step 203. This is because in order to encode the TFCI for the DSCH and the TFCI for the DCH in the same coding method, the MAC-D 303 must simultaneously transmit the DSCH scheduling information and the TFCI information to the L1 307 of the Node B. Therefore, when the MAC-D 303 has data to transmit, a delay occurs until the MAC-D 303 receives the scheduling information and the TFCI information from the MAC-C/SH 305 after transmitting the data to the MAC-C/SH 305. In addition, when the MAC-C/SH 305 is separated from the MAC-D 303 on the lur, i.e., when the MAC-C/SH 305 exists in the DRNC (Drift RNC) and the MAC-D 303 exists in the SRNC, the scheduling information and the TFCI information are exchanged on the lur, causing an increase in the delay.
Compared with the LSM method, the HSM method can reduce the delay because information transmission to the MAC-D is not required after scheduling in the MAC-C/SH. This is possible because the Node B can independently encode the TFCI for the DCH and the TFCI for the DSCH in the HSM method. In addition, when the MAC-C/SH is separated from the MAC-D on the lur, i.e., when the MAC-C/SH exists in the DRNC and the MAC-D exists in the SRNC, the scheduling information is not exchanged on the lur. Therefore, in some cases, it is not possible to use the LSM that must recognize the scheduling information. However, in the current 3GPP HSM, the information amounts (bits) of the TFCIs for the DCH and the DSCH are fixedly divided in a ratio of 5 bits to 5 bits, so that it is possible to express a maximum of 32 TFCIs for the DCH and the DSCH. Therefore, when there are 32 TFCIs for the DSCH, the HSM method cannot be used. In addition, when the LSM is used, i.e., when the MAC-C/SH is separated from the MAC-D on the lur, the TFCI for the DCH and the TFCI for the DSCH may not be correctly transmitted.